The invention relates to a new and improved needled fabric structure having increased fiber entanglement and a coherent fiber structure, the needled fabric structure utilizing a new method and needle machine having an improved means for controlling the feed of the web composite through the needling area.
In recent years, there has been considerable development in the needling of fibers to produce needled fabric structures. Generally the textile industry has found that density of a needled fabric structure may be increased by increasing the depth of needle penetration or by increasing the number of punches to which the web is subjected and this latter may be done by multi-passing of the structure through the loom. Of course, the fabric structure can only be punched a certain number of times; otherwise, it produces such a dense structure that it causes the needles of the needle loom to break or the structure itself to disintegrate with further needling.
To improve the fiber entanglement within a needled fiber structure and hence those physical properties based on the quality of fiber entanglement, it has been found that less depth of needle penetration through a fiber web and smaller advances between successive penetrations of a given needle must be used. With such improved fabrics, certain problems only vaguely recognized in the prior art become acute. Thus, in previous methods of needling fiber webs, the art has observed an undesirable surface pattern phenomenon which has been referred to as needle tracking. The visual effect is a series of linear scars of varying width and intensity running in the direction of machine feed. Because of the desirability of producing a product with a uniform surface, this linear surface effect has been investigated in detail, but the art has not been able to determine precisely the cause thereof. It is believed, however, that misplaced, bent, or irregular needles and/or the feed interval of the fiber web contribute to the tracking phenomenon.
An article, "Needled Nonwovens: The Problems Of Tracking" Part I-Cause And Effect and Part II-Some Solutions by G. Young appearing respectively in the Feb. and Mar., 1970 issues of "Textile Month" printed in England at the Buxton Press, Buxton, Derbyshire, describes considerable research effort directed toward determining the cause of such linear surface tracking and accordingly developing methods of obviating the same. While no definite solutions to the problem of tracking were found, the results show that tracking becomes more acute as the distance between successive needle punches of a particular needle decreases, i.e., as the number of successive needle punches per linear inch increases. Accordingly, in order to somewhat mitigate the problem, the Young reference indicates that large distances between successive needle punches should be practiced. Further, Young indicates that by moving the web of fibers laterally with respect to the feed direction, the nature of tracking can be affected. However, the tracking still exists and, essentially, only the surface appearance is changed.
In a manner somewhat similar to the suggestion of Young, U.S. Pat. No. 3,535,756 to Kuts et al, issued Oct. 27, 1970, suggests oscillating a web during the needling operation whereby lateral movement of the web is accomplished by the draw-off rolls of the needle loom. The web is held, essentially, in a tensioned condition during the needle operation by means of a restrictive inlet throat guiding the web into the needling area. However, so far as the Kuts et al method is concerned, conventional distances between successive needle punches are practiced in conventional machines using conventional methods. The conventional distance between successive punches of a given needle would be normally at least one-quarter inch. As illustrated by Young, these longer distances between successive needle punches in and of themselves tend to mitigate linear tracking. Likewise, Kuts et al does not propose his method for mitigating tracking for needle processes which utilize distances between successive needle punches other than the conventional distances.
As an alternate proposal in the art, U.S. Pat. No. 3,150,434 to O'Byrne, issued Sept. 29, 1964, suggests intermittently moving a web of fibers through a needling area and reciprocating the web during passage thereof through the needling area. Here again, conventional distances between successive needle penetrations are envisioned.
As can be appreciated from the above brief summaries of the relevant prior art, the effort to improve surface appearance by reducing needle tracking has assumed conventional distances between successive needle penetrations of a particular needle, i.e., normally at least one-quarter inch.
Unfortunately, these conventional distances between successive needle punches of a particular needle are not always capable of producing a superior fiber entanglement and coherent fiber structure which is desired for some products and, therefore, short advances between successive penetrations of a given needle are necessary. Tracking in these superior needled fabrics presents a far more serious problem than that which existed with the prior conventional needled fabrics, where appearance was the primary consideration.
While not bound by theory, it is believed that the fiber involvement by a relatively short distance between successive needle penetration so orients the fibers of the needle batt that succeeding needles are, in effect, guided again into the previously needled areas and intensify the tracking difficulty. Thus, with the shorter distances between needle penetration, the tracking produces rows of densely needled fibers separated by areas of considerably less needled fibers, similar to the appearance of a plowed field.
While surface linear tracking of the aforenoted nature in these superior products is not necessarily undesirable for some applications, it should be appreciated that such tracking affects the interior of the fiber structures and can produce non-uniformities of properties which often become evident when the needled fabric is subjected to stress. In order to mitigate the tracking of this nature in these superior products, it has been found that special means are necessary for reducing the tendency of successive needles to follow in the path or track of earlier needles. Briefly, it is necessary that the needling with the short distances between successive needle penetrations be performed while the web is under relatively low tension and preferably under the minimum tension required for reasonably uniform feeding of the fiber web into and through a needling loom. Additionally, the web must be free to move transversely while passing through the needling zone. Also, it is important and preferred that the movement in the transverse direction decreases, generally, in amplitude as the web passes through the needling zone. With such provisions during the needling operation, the tracking noted above may not only be substantially mitigated, but it has been additionally discovered that the needling effectiveness, as indicated by the physical properties of the resulting fabric, is significantly increased.
For purposes of the present specification, the relatively short distances between successive needle penetrations are herein defined as those distances which allow a successive needle penetration to involve fibers involved by the previous penetrations. Generally speaking, involvement of fibers of the foregoing nature will be accomplished when at least seven needle penetrations per linear inch are performed by a particular needle.